When the phone is in standby mode with a black screen, many circuits are not working, that is, they are not powered. When the power button is pressed to wake up, some circuits of the phone start to work, which may cause the subsequent powered circuits to short-circuit and burn due to water ingress.
What we need to do after the phone gets soaked in water is to disassemble the phone. First, we need to cut off the power, that is, cut off the connection between the battery and the motherboard, and then use the dryer to blow dry the water until the water is no longer visible, and then use the hot air to heat the motherboard back and forth evenly (note that the dryer should not be too close to the motherboard to keep more than 5cm), heat for 5 to 10 minutes and cool naturally. After the motherboard cools down, you can try to install the battery to start the machine for testing. Generally, this is the solution for non-serious water ingress.
If the phone is severely flooded, you can simply cut off the power and perform the above steps before going to a professional repair shop for testing and treatment. Do not operate blindly to avoid causing more serious problems to the phone.